I realize this is nitpicky, but, taken literally, the definition you currently have implies that a show’s “jump the shark” episode is its best, with the idea that every episode after that is not quite as excellent. However, the term was originally used to denote a spectacularly bad episode in a formerly enjoyable series, with the idea that that all subsequent episodes were, or are likely to be, of poor quality as well. The jump the shark momement generally occurs well after a show has reached, and passed, its peak, and refers to the moment that a show has reached such a low point that it is no longer enjoyable. (I suppose a show could reach its peak in one episode and jump the shark in the very next episode).
The original idea was to try to pinpoint the exact moment that a series crossed the threshold from worth watching to not worth watching. Since then, use of the term has broadened, and it often simply refers to the idea that a series isn’t any good anymore, with no particular episode being identified as the tipping point. And, of course, no discussion of jump the shark is complete without a gratuitous joke about whether the expression itself has jumped the shark. I find it a silly but mildly amusing phrase, and am neither a staunch defender of it nor particularly bothered by it.

No, the original intent as outlined by the phrase’s coiners was that moment of peak popularity/quality. The Happy Days episode in which Fonzie literally jumped the shark was the peak of the series’s popularity.

And I originally intended to stop at the century, but then I decided “what the hell, I’ve come this far...”

And if I figure out a way to do the future, I’m not going to post it here. I’ll sell out to Wall Street.

No, the original intent as outlined by the phrase’s coiners was that moment of peak popularity/quality. The Happy Days episode in which Fonzie literally jumped the shark was the peak of the series’s popularity.

I don’t think it’s as clear as you make it out to be. Here’s Wikipedia‘s account (and yes, it’s Wikipedia, but it certainly sounds well-researched and has a number of footnoted references):

Jumping the shark is an idiom created by Jon Hein that is used to describe the moment in the evolution of a television show when it begins a decline in quality that is beyond recovery. The phrase is also used to refer to a particular scene, episode or aspect of a show in which the writers use some type of “gimmick” in a desperate attempt to keep viewers’ interest.

In its initial usage, it referred to the point in a television program’s history when the program had outlived its freshness and viewers had begun to feel that the show’s writers were out of new ideas, often after great effort was made to revive interest in the show by the writers, producers, or network.

[...]

The phrase jump the shark comes from a scene in the fifth season premiere episode of the American TV series Happy Days titled “Hollywood: Part 3”, written by Fred Fox, Jr. and aired on September 20, 1977. In the episode, the central characters visit Los Angeles, where a water-skiing Fonzie (Henry Winkler), answers a challenge to his bravery by wearing swim trunks and his trademark leather jacket, and jumping over a confined shark. For a show that in its early seasons depicted universally-relatable adolescent and family experiences against a backdrop of 1950s nostalgia, this incident marked an audacious, cartoonish turn towards attention-seeking gimmickry. Initially a supporting character, the faddish lionization of an increasingly superhuman Fonzie became the focus of Happy Days. The series continued for nearly five years after Fonzie’s shark-jumping stunt, with a number of changes in cast and situations. However, it is commonly believed that the show began a creative decline in this era, as writers ran out of ideas and Happy Days became a caricature of itself.

In 1997, Hein published his list of approximately 200 television shows, and his opinions of the moments each “jumped the shark.” The site soon became an internet phenomenon, and as the phrase quickly spread all throughout pop culture the site grew exponentially in users and renown. Hein subsequently authored two “Jump The Shark” books and later became a regular on The Howard Stern Show around the time he sold his website to Gemstar (owners of TV Guide).

In a 2010 Los Angeles Times article, former Happy Days writer Fred Fox Jr., who wrote the episode that later spawned the phrase, said, “Was the [shark jump] episode of Happy Days deserving of its fate? No, it wasn’t. All successful shows eventually start to decline, but this was not Happy Days‘ time.” Fox also points to not only the success of the episode itself ("a huge hit” with over 30 million viewers), but also to the continued popularity of the series.

My takeaway from this is that the phrase was indeed created with the general meaning Svinyard describes (though not necessarily “a spectacularly bad episode,” but one that marks an irreversible turn for the worse). Your reaction mirrors that of Fox, which (however understandable for the show’s writer) is not to the point: the term was created by Hein, not Fox, and I have never seen it used in any other way than Hein’s, however distressing that may be for Fox and fans of the show.

The “gimmickry” and “desperate attempt to keep viewers’ interest” are read into Hein’s definition by others. In a 1999 NY Times article Hein is quoted as saying, “In my opinion, there is a definitive moment in every show when that happens, when it goes downhill. After that the program will never be the same again.” Jumping the shark, according to Hein, is simply the moment when the show takes a downward turn from its peak, it may or may not be spectacularly bad or involve gimmickry.

My main point, which I agree I overstated, is that a show’s “jump the shark” moment is not the peak of its quality. A show has already begun its decline in quality, and, thus, passed its peak, the moment it has jumped the shark.

The 2001 entry defines jump the shark as the peak of a show’s quality and popularity. As to quality, i don’t see how a jump the shark moment could be the show’s peak.

As to popularity, the jump the shark momement may or may not be the show’s peak, but it wouldn’t be surprising if it was (since, broadly speaking, an episode is unlikely to negatively affect the series’ popularity until AFTER people have watched it). As far as I can tell, the coiner of the phrase was concerned with identifying the moment that a show dropped in quality/enjoyability, and the term didn’t really convey an assessment, one way or the other, as to whether the show was at its peak in popularity.

My main point, which I agree I overstated, is that a show’s “jump the shark” moment is not the peak of its quality. A show has already begun its decline in quality, and, thus, passed its peak, the moment it has jumped the shark.

I think the ‘jump the shark’ moment is necessarily both the peak and the moment from which it begins to decline. If the show had begun to decline earlier then we’d have to push the JTS moment back, unless you’re going to redefine the phrase.

Huh? I don’t understand that argument at all. In my experience, it’s far more likely that the peak—the best episodes of a show—occur in one season (for the sake of argument, season 3) and next season it starts falling off, for complex reasons I’d understand better if I’d ever worked in television. At any rate, the shark moment—the moment it clearly goes off the cliff—is going to happen in that later season, not in the last great season.